If a User Equipment (UE) is Global Navigation Satellite (GNSS) enabled, e.g., a Global Positioning System (GPS) enabled, then the current position of the UE can be obtained directly using the GPS, which can be referred to as standalone GNSS positioning.
Since the GNSS is costly, and a GNSS signal significantly fades in an indoor scenario, the scheme of cellular network signal or cellular network aided positioning of the UE has been proposed in the prior art, i.e., the Location Service (LCS).
FIG. 1 illustrates a flow of positioning in the control plane of the LTE LCS, where the flow includes the following steps:
1. A Mobility Management Entity (MME) receives a location service request, which can be a request initiated by the UE to the MME in a Non Access Stratum (NAS) message, or a location service request initiated in some entity (e.g., a Gateway Mobile Location Center (GMLC)) in an Evolved Packet Core (EPC), or the MME.
2. The MME transmits the location service request to an Evolved Service Mobile Location Center (E-SMLC), and the E-SMLC selects an appropriate positioning scheme according to a Quality of Service (QoS) including accuracy and time-delay of positioning, carried in the location service request.
3a. The E-SMLC may trigger an evolved Node B (eNB) related positioning procedure as specified in the LTE Positioning Protocol Annex (LPPa), for example, obtain assistance data required for positioning, or a measurement required for positioning;
3b. The E-SMLC may trigger a UE related positioning procedure as specified in the LIE Positioning Protocol (UV), for example, obtain a position estimation, assistance data required for positioning, or a measurement required for positioning;
4. The E-SMLC transmits a location service response including some desirable results, e.g., the position of the UE, a positioning success or failure indicator, to the MIME; and
5. The MME returns the location service response to a target entity.
Positioning schemes supported for positioning in the control plane will be briefed below.
The existing positioning schemes supported for positioning in the control plane of the LTE LCS includes the following options:
Firstly the position of the UE is calculated according to known serving cell geographical information together with other measurement information based upon a cell identifier (ID), e.g., in the Time Advance (TA) plus Angle of Arrival (APA) scheme;
Secondly the UE listens concurrently to pilot signals of a number of eNBs, obtains the difference in time of arrival between the signals of the eNBs, and determines the position of the UE in more than two hyperbolic equations, e.g., in the Observed Time Difference of Arrival (OTDOA) and in the Uplink Time Difference of Arrival (UTDOA) scheme; and
Thirdly there is a scheme of network assisted positioning by a global satellite navigation system including a GPS system, a Galileo system, or another available positioning system. In the A-GNSS scheme, the workload of UE is operationally simplified in that a position calculation center at the network side interoperates with the UE to position the UE. For example, the network side can estimate from the preliminary position of the UE an operating condition of a satellite above the position, e.g., ephemeris, almanac, and differential calibration, and other information, and transmit the operating condition to the UE. The UE can optimize searching and positioning procedures using the operating condition as priori knowledge to thereby achieve the effects of shortening a period of time for searching, lowering the required level of a search signal, and other effects so as to improve the performance of positioning.
As smart phones are being popularized, business opportunities of indoor positioning are gradually emerging, but also faced with their challenge, for example, currently widely GPS positioning may not position successfully the smart phone indoors due to the unavailability of a satellite signal; and if the smart phone is positioned indoors using a cellular network signal, then the smart phone may be positioned less precisely in the indoor NLOS environment. Consequently other positioning schemes may be introduced in addition to the several existing positioning schemes for positioning in the LTE control plane.
There is a scheme of positioning based upon a WLAN signal. At present a WLAN is deployed by an operator to offload cellular network traffic, so the UE can be positioned indoors more precisely over the deployed WLAN.
There is a scheme of positioning using a Pseudo-Satellite or Pseduolite (PL). In response to a demand for indoor positioning, some transmitter is arranged indoors on the ground to transmit some positioning signal, which is typically a GPS-like signal, so that the UE can receive the pseudo-satellite signal for indoor positioning.
In summary, there are a number of positioning schemes supported for positioning in the LTE control plane, and the number of supported positioning schemes may be increasing along with subsequent evolvement of the technologies. The surrounding environment of the UE while moving may be changing constantly so that the appropriate positioning schemes available to the UE may also be changing. For example, if the outdoor UE grooves into a shopping mall in which there is an offloading WLAN in addition to a cellular eNB, then the A-GNSS positioning scheme applied outdoors to the UE may not be available, but the UE will be positioned over the WLAN; or if the UE moves from an indoor environment in which only a cellular eNB is deployed, to an indoor environment in which a pseudo-satellite is deployed, then the UE will be switched from the scheme of positioning using the cellular eNB to the scheme of positioning using the pseudo-satellite for a more precise result of indoor positioning. There has been absent so far a feasible solution to seamless switching of the positioning scheme for the UE to be positioned in the control plane.